My $9 shipped from DX trustfire TR-001 charges right to 4.2V. I have left batteries on it overnight, by accident, and they were right at 4.2V and cool to the touch. However, I'm always in close proximity when I charge my cheap batteries with my cheap charger and I try to take the batteries off right when the light turns green because it's just easier to be safe than on fire, or exploded, or any of the other horror stories I've heard.

My $9 shipped from DX trustfire TR-001 charges right to 4.2V. I have left batteries on it overnight, by accident, and they were right at 4.2V and cool to the touch. However, I'm always in close proximity when I charge my cheap batteries with my cheap charger and I try to take the batteries off right when the light turns green because it's just easier to be safe than on fire, or exploded, or any of the other horror stories I've heard.

Excellent point, and very valuable info that you've presented to our community.

^^^^^ That's the one I have! Funny. I'm going to keep keeping my eye on mine. I've had it over 2 years w/no problems. It looks like the one in the picture burned up right where the main a.c. power goes in.

Every green laser I've had is positive towards tailcap, negative to module

I am not trying to scare people, just to make them aware. What could happen.

I also do not advocate against any particular company for now.

I used to sell over 14 different types of li-ion chargers, with various results.

Basic rules (from my experience)

If you can have both - it is the best option- but either one would significantly decrease your risk of using fire extinguisher

1. Li-ion battery must be top of the line battery. (do your research - there are many battery tests/reviews available)
2. Charger must be designed with safe charging in mind. (fewer reviews, but still good starting point for using best charger)
3.Go to batteryuniversity.com, to help you understand even more.

You follow these basics, and you will be on the safe side.

Do your research on batteries / chargers (forums about batteries and flashlights are good place to start - there are some highly respected forums discussing batteries and chargers in depth ) .

Quite unusual approach to safety related issue. But that's your opinion.
I would never recommend to any new user to do that - having in mind that 100s of battery chargers, and batteries (known, and unknown) being sold to the worldwide market.

This text below (from batteryuniversity.com) is very valuable piece of info for people who do care about safety.

Overcharging Lithium-ion

Lithium-ion operates safely within the designated operating voltages; however, the battery becomes unstable if inadvertently charged to a higher than specified voltage. Prolonged charging above 4.30V forms plating of metallic lithium on the anode, while the cathode material becomes an oxidizing agent, loses stability and produces carbon dioxide (CO2). The cell pressure rises, and if charging is allowed to continue the current interrupt device (CID) responsible for cell safety disconnects the current at 1,380kPa (200psi).
Should the pressure rise further, a safety membrane bursts open at 3,450kPa (500psi) and the cell might eventually vent with flame. The thermal runaway moves lower when the battery is fully charged; for Li-cobalt this threshold is between 130–150C°C (266–302°F), nickel-manganese-cobalt (NMC) is 170–180°C (338–356°F), and manganese is 250°C (482°F). Li-phosphate enjoys similar and better temperature stabilities than manganese.
Lithium-ion is not the only battery that is a safety hazard if overcharged. Lead- and nickel-based batteries are also known to melt down and cause fire if improperly handled. Nickel-based batteries have also been recalled for safety concerns. Properly designed charging equipment is paramount for all battery systems.

brenner: the problem is that many chargers look exactly alike, but have different internals. Not to mention, I can only think of one charger that is reputed to charge cells correctly. Most of the rest are just CV. Best way would be to charge them yourself, but then that would require people to (gasp!) learn.

in the end, I generally just suggest people avoid Lithium anything in multi-cell lights, and if I have to recommend something, it is protected cells and a Pila IBC. No first-hand experience with the IBC, but it is reputed to actually use CC up to 4.2V, and then hold the voltage at 4.2 until current diminishes to a predetermined threshold.